In recent years, as a result that a variety of electronic apparatuses have become more compact, electronic devices to be installed inside the electronic apparatuses have been made furthermore compact and to have higher performance. As one of the electronic devices, there is a multilayer ceramic capacitor, which has been also required to be more compact and to have higher performance.
To pursue attaining of a more compact multilayer ceramic capacitor with a higher capacity, dielectric layers are strongly required to be thinner and, recently, a thickness of a dielectric green sheet for forming the dielectric layers after firing is also made thin as several μm or thinner.
To produce a dielectric green sheet, normally, green sheet slurry formed by a dielectric powder, binder, plasticizer and organic solvent (toluene, alcohol and MEK, etc.) is prepared first. Then, the green sheet slurry is applied to a carrier film, such as PET, by using the doctor blade method, etc. and heated to dry.
In recent years, a method of preparing a ceramic suspension obtained by mixing a dielectric powder and a binder in a solvent and performing biaxial stretching on a film-shaped mold obtained by performing extruding on the suspension has been studied.
A method of producing a multilayer ceramic capacitor by using the ceramic green sheet as above will be explained. Internal electrode paste including a metal powder and a binder is printed in a predetermined pattern and dried to form an internal electrode pattern. Next, a carrier sheet is removed from the ceramic green sheet, and the results are stacked and cut into a chip shape to obtain a green chip. Then, after firing the green chip, external electrodes are formed.
However, when directly printing the internal electrode paste on the green sheet, a solvent in the internal electrode paste soaks into the green sheet and a phenomenon called a sheet attack arises. The sheet attack due to soaking by the solvent causes pin holes on the green sheet and often causes short-circuiting defects. Particularly, when the dielectric green sheet is formed to be extremely thin, effects of the sheet attack become notable, so that an interlayer thickness of the sheet has been hard to be made thin.
On the other hand, in the patent articles 1 to 4 below, a dry type electrode pattern is separately prepared by forming an internal electrode pattern on a support sheet and drying. And an internal electrode pattern transfer method for transferring the dry type electrode pattern to a surface of each dielectric green sheet or a surface of a multilayer body of the dielectric green sheet has been proposed.
In the technique described in the patent articles 1 to 4, however, particularly when a thickness of the green sheet is thin, there have been problems that it is extremely difficult to bond an electrode pattern layer with a surface of the green sheet well and transfer with high accuracy and, in the transfer step, the dielectric sheet partially breaks and results in arising a short-circuiting defect. Furthermore, when the green sheets each having an electrode pattern layer formed thereon directly stacked as in the patent articles 1 to 4, there has been a problem that an adhesive force between the internal electrode formation surface and the green sheet surface becomes insufficient to cause adhesion defect.
To eliminate the nonadhesion defects and short-circuiting defects, for example, the patent articles 5 to 7 disclose a method wherein a green sheet configured to be sandwiched by green sheet layers from the above and below is formed as a green sheet having an internal electrode pattern and stacked. In the method described in the articles, for example, green sheet layers having about a half thickness of a desired thickness are bonded and the desired thickness (a thickness of one layer) is attained. In this method, green sheets layers are bonded when stacking, so that an adhesive force between the sheets can be improved and short-circuiting defects caused by a pin hole can be reduced. However, in this method, the green sheet layer has to be made extremely thin as about half thickness of the desired thickness, so that it has been difficult to respond to demands for further thinner layers.
Also, the patent articles 8 to 13 disclose a method wherein a green sheet formed by overlapping two or more green sheet layers is used as a green sheet having an internal electrode pattern and stacked. These articles describe that short-circuiting defects and delamination can be suppressed. However, in the method disclosed in these articles, each green sheet layer has to be furthermore thinner when making the green sheet itself thinner, so that it has been difficult to respond to demands for a further thinner green sheet.
Particularly, in these articles, a green sheet formed by overlapping two or more green sheets each having a thickness of several μm or so is used. Namely, 2 to 3 layers of green sheets each having a thickness of 2 to 3 μm or so in the patent articles 5 and 6, two green sheet layers having a thickness of 6 to 7 μm or so in the patent articles 7 and 8, a green sheet layer having a thickness of 3 to 3.4 μm or so and a green sheet layer having a thickness of 0.6 to 1 μm were overlapped to form a green sheet in the patent articles 9 and 10. Therefore, it has been difficult to respond to demands for further thinner layers for these articles.
Patent Article 1: The Japanese Unexamined Patent Article No. 63-51616
Patent Article 2: The Japanese Unexamined Patent Article No. 3-250612
Patent Article 3: The Japanese Unexamined Patent Article No. 5-159966
Patent Article 4: The Japanese Unexamined Patent Article No. 7-312326
Patent Article 5: The Japanese Unexamined Patent Article No. 7-297073
Patent Article 6: The Japanese Unexamined Patent Article No. 2004-103963
Patent Article 7: The Japanese Unexamined Patent Article No. 2004-119802
Patent Article 8: The Japanese Unexamined Patent Article No. 10-50552
Patent Article 9: The Japanese Unexamined Patent Article No. 11-144992
Patent Article 10: The Japanese Unexamined Patent Article No. 8-37128
Patent Article 11: The Japanese Unexamined Patent Article No. 5-101970
Patent Article 12: The Japanese Unexamined Patent Article No. 2003-264120
Patent Article 13: The Japanese Unexamined Patent Article No. 2003-272947